Vikings. Attila the Hun. Cavemen. Meet the in-laws, or rather, those genetic relatives you didn't expect to find on your family tree.

Amid the wonders of the age of genetics, people worldwide are spitting, swabbing or otherwise submitting samples to genetic registries, opening an era in understanding that most fundamental of questions: Who am I?

"Everyone wants to know how much of a Neanderthal they are," says genetics expert Spencer Wells, head of National Geographic's Genographic Project, a worldwide DNA ancestry-tracing effort that estimates how related you are to that vanished family of human caveman cousins. "Wives particularly seem interested in their husband's results, for some reason," Wells jokes.

Once the domain of great-aunts hunting down any family member with a royal pedigree, the world of genealogy is tapping into the genetics revolution while going mainstream. In less than a decade, more than a million people have taken such ancestry tests, offered by more than two dozen companies. The Genographic Project got things going in 2005. The "incredible response," Wells says, reflects a revolution in cheaper DNA testing, one that has at times raised hackles of privacy advocates.

At the National Genealogical Society's annual meeting last month in Las Vegas, more traditional talks on tracing immigrant paperwork competed for attention with a new slate of "DNA" sleuthing from geneticists.

A woman participates in National Geographic's Genographic Project in Queens, N.Y.(Photo: Hatnim Lee, National Geographic)

Indeed, the ancient art of family-tree-tracing is rushing into the 21st century.

"We are seeing a coming of age in genealogy meeting genetics," says Ancestry.Com's Ken Chahine, a biochemist. "The expense of tests has dropped, and the number of records has reached a point where we are able to tell people a good deal about their ancestry."

Intended by National Geographic as a part of its mission to map and explore the world, the Genographic Project has analyzed the genetic markers of nearly 600,000 people since 2005, specializing in looking to the origins of modern humans in Africa more than 100,000 years ago.

Those include links to our ancient cousins, the Neanderthals, whose genome or gene map was first published by researchers in 2010. Svante Paabo of Germany's Max Planck Institute for Evolutionary Anthropology completed the task. Anyone who isn't African probably shares about 2% to 3% of his or her genes with Neanderthals, it turns out.

The project's success has spawned competitors.

The genealogy-focused Ancestry.Com's AncestryDNA has more than 120,000 test takers in its records, while the medically focused 23andMe, based in Mountain View, Calif., has tested more than 200,000 of its own. Not without critics, these gene-testing services and others offer genetic peeks into the past for people willing to buy kits that typically range in price from $99 to $199.

CLUES TO YOUR PAST

What do people learn from the tests? They can't tell a Spaniard from an Italian yet, Chahine says. Instead they tell people where — geographically — their distant ancestors originated, as judged from where their gene markers appear most abundantly in modern populations.

AncestryDNA focuses on the more recent past, "where your ancestors lived hundreds — perhaps even thousands — of years ago," its website says. Results are divided into geographic areas such as Scandinavia or Southern Europe, then distant genetic cousins can be located in the company's database. You might be told you have Vikings or Romans in your past, but don't get too excited. Pretty much everyone does.

The tests can't tell you whether Marie Antoinette or someone equally famous was a cousin because most genes are shared broadly across humanity. Go back more than a few generations, and humans share millions of common ancestors.

Despite that common thread, these tests can take you to many surprising places. For instance, 23andMe scours its results looking for about 100 markers for congenital diseases — as well as documenting Neanderthal genes. The Genographic Project, while also noting one's Neanderthal roots, delivers a lesson in the ancient In-and-Out-of-Africa genetic migration that started more than 65,000 years ago. It ends with a summary of where a person's genes most recently resided — a picture that grows hazy within the past 5,000 years.

"Most of the time, people see the results they might expect to see from their ancestry," Wells says. "But we are also telling people a lot about how genes work and what they can and cannot tell them about the past."

'GENETIC ASTROLOGY' OR SCIENCE?

Critics say some tests are doing a disservice. In March, the United Kingdom's "Sense About Science" campaign published a booklet warning against expensive genetics tests that claimed to link people to history's famous folks, such as the Queen of Sheba or Napoleon. They call such claims "genetic astrology" because going back a few generations, everyone starts to look related.

A May 7 study in the journal PLOS Biology found that every European is likely to share "millions" of common ancestors within the past 1,000 years even with someone on the opposite side of the continent, making a connection with a Hun or Viking hard to miss in most European family trees.

But not all of this testing is frivolous. "The rapidly enlarging genetic genealogical databases have in recent years become increasingly useful to scientists," notes a research team led by Maarten Larmuseau of Belgium's Katholieke Universiteit Leuven in an American Journal of Physical Anthropology review published this year.

A 23andMe team reported 20 new genetic markers linked to nearsightedness among people with a European background in March. In an April study, data from the Genographic Project were compared with DNA taken from ancient skeletons. The researchers found that an unsuspected migration of farmers from Spain into Central Europe took place around 2,800 B.C.

As with much of the DNA and genetic testing world, these scientific efforts raise privacy worries.

Gene detectives from the Whitehead Institute for Biomedical Research in Cambridge, Mass., reported in January that they could guess the identity of 12% of men in an anonymous database by comparing their data with information in genealogical gene records. Rebecca Skloot, author of The Immortal Life of Henrietta Lacks, has noted that scientists were blithely publishing the gene map of the subject of her book without any permission from her family. After she died in 1951, Lacks' cells were widely used in cancer studies.

"Definitely the field is aware of privacy concerns, more aware even than we started," Chahine says, noting the AncestryDNA effort lets people keep their results anonymous to the outside world.

A federal law, the 2008 Genetic Information Nondiscrimination Act (GINA), specifies that insurers and employers can't discriminate against people because of their genetic makeup. However, Yaniv Erlich of the Whitehead Institute for Biomedical Research, notes that keeping your individual gene map private doesn't mean it can't be pieced together from the publicly available maps of your relatives. If a distant relative of yours makes their genes available in a public database, analysts might be able to learn about your genes simply by knowing your last name.

Of course, the tests might still need a little work.

In April, Kate Wong, the anthropology editor of Scientific American, reported that one company's test found she was 2.1% Neanderthal, while another determined she was 2.9% related to the ancient human species — a considerable difference in the world of science. So even the tests for our genes aren't perfect, which is to be expected. Scientists, after all, are only human.

ANCESTRY TESTS

More than two dozen genetic ancestry tests are on the market, among the best known:

• 23andMe — The Mountain View, Calif., service, used by more than 200,000 people since 2006, aims to combine medical and ancestry information, checking for more than 240 health conditions or traits linked to genes through a $99 test. The company name is a nod to the 23 human chromosome pairs.

• AncestryDNA — Tied to the Ancestry.com genealogy company based in Provo, Utah, the $99 test focuses on what genes say about your family history in the past few thousand years and links its 120,000 users to about 40 million family trees in the company's records.

• National Geographic's Genographic Project — Since 2005, nearly 600,000 participants have used the $199.95 test, which focuses on both recent and ancient ancestry, constructing a timeline-driven map of where paternal and maternal lineage genes originated.

All of these ancestry services include online tools for finding cousins and near-relatives with similar genetic profiles who have also taken such DNA tests.

National Geographic's 'Genographic Project', a DNA ancestry tracing effort for humanity, has announced a new initiative to add more participants and more genes to its map of human origins. Here, a Chadean man from the Saharan Desert recorded on a project expedition. (Photo: Nat. Geo. - David Evans)

The Genographic project traces ancient human migrations and reveals deep ancestry to participants, including ties to our early human cousins, the Neanderthals and Denisovans as well as early modern humans who first originated in Africa. (Photo: National Geographic)

Our genes, encoded in DNA represented by this illustrative strand, contain unique information about each person's ancestry revealed by comparing ones shared among people from different locales. (Photo: IBM)

Regular project participants pay $200 for a kit that includes swabs and a mailer to send off a skin sample, which is added to global DNA records and reveals their own deep ancestry. (Photo: Rebecca Hale/National Geographic)